Electric amplifier



March 9, 1937.. L. c. VERMAN E'l AL v 2,073,234

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EXUTER M/MN H ALTERNATOR B2 43 f E i E I 4E 53 47 TI] EuMmATuR INPUT W /4E R f LAL ags a EUMINATDR DUTF'UT J BY LBRENZB A-RI HARDS ATTORNEY Patented Mar. 9, 1937 UNITED STATES PATENT OFFICE ELECTRIC AMPLIFIER Original application June 5, 1931, Serial No. 542,294. Divided and this. application March 17, 1933, Serial No. 661,332. In Great Britain June 6, 1932 6 Claims.

This application, which is a division of United States application Serial No. 542,294 filed June 5, 1931, now Patent No. 2,021,061 issued November 19, 1935, relates to novel methods and ap- 5 paratus for amplifying signals and more particularly for operating direct current vacuum tube amplifiers such as for use in regulating systems or other cases where it is desired to amplify relatively slowly occurring variations of electric l currents or potentials.

The invention is specifically applicable to regulation of electrical or other physical quantities which may be transformed into corresponding electrical variations including temperature,

15 speed, light, sound, etc.

More specifically, our invention concerns a new type of direct coupled vacuum tube cascade amplifier in which a direct and conductive coupling connection is provided from one amplifying tube 20 to a succeeding amplifying tube.

An object of the invention is to provide a direct coupled cascade amplifier of the aforementioned type in which the variation of the output potential is in any desired sense or phase 25 relative to the phase of the input potential variation applied to the amplifier.

In amplifiers of the aforementioned type as known in the prior art using a direct conductive coupling connection from the anode or output '30 electrode or" one amplifying tube to the grid or control electrode of the succeeding amplifying tube, a reversal of the phase of the output potential variations relative to the phase of the input potential is obtained in a single stage. This 35 makes it necessary to use an even or odd number of stages when it is desired to obtain an input potential having the same phase as the input potential or having opposite phase relative to the input potential, respectively.

40 Accordingly it is an object of our invention to provide a new circuit of direct coupled amplifying system in which the phase relationship of output potential relative to the input potential is reversed, as compared to amplifiers of standard design known in the art, in such a manner as to enable the use of a proper combination of either an even or odd number of amplifying stages coupled both according to the old or the new 50 manner with a view to obtaining any desired phase relationship between input and output po- I tential of the amplifier, as may be desired in any particular instance, such as in regulating or controlling systems where the controlling or output 55 variation of the amplifier has to be in a predetermined sense to secure proper controlling or regulating action on the device under control.

These and further objects as well as aspects of our invention will become more apparent from the following detailed description taken with reference to the accompanying drawing by which we have illustrated our invention by way of example as applied to a voltage regulating system for an alternating current generator. It should be understood, however, that the embodi- 10 ment of the invention to be described is to be regarded as illustrative only of the broader principle of the invention as expressed in the appended claims.

Figure 1 schematically illustrates the operation of a regulating system which may include an amplifier of the type according to the invention.

Figure 2 illustrates a regulating system for an electric generator embodying an amplifier of the type known according tothe art; and

Figure 3 shows another system for maintaining constant the voltage of an alternating current generator and embodying the novel type amplifier in accordance with our invention.

Similar reference numerals identify similar parts throughout the different views of the drawing.

Referring to Figure l, the system i which may be of any physical form and which is to be controlled, is connected to a control element 2 which translates a variable physical condition into corresponding electrical variations. These electrical variations are applied to the amplifier 3 which amplifies these electrical variations and the amplified variations are applied to the correcting apparatus 4. The correcting apparatus is actuated by the amplified variations and reacts on the system which is to be regulated in such a Way as to correct the deviations from the normal condition.

Figure 2 shows a schematic circuit diagram with a voltage regulator for a direct current generator 5 connected across the lines 8 and 1. Also connected across the lines 6 and 1 and therefore responsive to the voltage fluctuation thereof, are the fixed resistor 8 and in series therewith, the variable resistance 9. Resistor 9 is so adjusted that the drop of potential through the resistor 8 is nearly equal to the potential of the battery I0 which is connected in series with the resistor 8 and across the input of a three-element tube l2. The side of the resistance 8 which is connected through resistance 9 to the negative side of the generator 5, that is to the line I, is also connected I2, the potential of the filament of tube battery I is in bucking relation with the potential across the resistance 8.

Accordingly, the difference between the potential drop in the resistor 8 and the voltage of the battery H3 is impressed across the input circuit of the three-element tube I2 including the grid I3 and the cathode I4 in such a manner that the potential of grid I3 becomes more or less negative as the drop through the resistor 8 de creases or increases.

The voltage generated by the battery III is substantially constant and accordingly the variations of potential across the input are due to the variations in the voltage drop of resistance 8 which in turn is a direct function of the changes in potential across the lines 6 and I or of the generator 5. The output currents of the tube I2 flow over the plate I5 which is directly connected to the grid of the second three-element tube Hi. The plate circuit of the threeelement tube I6 is connected through a measuring instrument 5? to one side of the field winding I8 of an exciter 26. The other side of the field winding I8 is connected to the positive side of a resistance element 2I.

The amplifier circuit disclosed in this figure is of the so-called direct coupled type in which the plate of the tube I2 is connected conductively directly to the grid of the next succeeding tube. A source of energy of any well-known form necessary for supplying a desired voltage across the potentiometer 2I is applied thereto through a pulsation eliminating filter of any well known construction over the conductors 22 and All of the necessary potentials for the various electrodes of the tubes I2 and I6 are obtained from taps taken from the potentiometer 2|. A resistance 24 is interposed between the lead connection to the plate I5 and a tap point 25 on the potentiometer 2|.

Inasmuch as the grid of the second tube I6 is of the same potential as the plate I5 of tube I6 must also be proportionately greater and within the range of the potential of its associated grid. Accordingly, the filament of tube I6 obtains its potential over the conductor 21 which is tapped to a predetermined point on the resistance 28 in turn connected between the taps 25 and 29 of potentiometer 2I.

The tap on resistance 28 and the tap at 29 are selected so that the filament potential of tube I6 is at a proper value with respect to the grid voltage of tube 56, such that the tube I6 will act as an amplifier for the impressed input currents. In this circuit the resistance 24 acts as the coupling resistance between the tubes, I2 and I6.

The filaments of tubes I2 and I6 are heated by alternating current supplied through independent transformers 3I and 32, the primaries of which are connected to 110 volt supply 33. The 110 volt supply 33 also controls a motor 34 which drives the exciter 20.

The operation of this circuit will now be obvious. In response to variations in voltage across the lines 6 and I caused by changes in the voltage of the main generator 5, there are instantaneous changes in the voltage applied across the input of tube I2. In response to these variations in input voltage across the tube I2, there are corresponding variations in the output of tube I2 which are applied to the input of tube I6, which in turn produce variations in the output tube I6. These output varia tions vary the current flowing through the field winding I8 of the exciter 20, and cause corresponding variations of the voltage generated by the exciter 20. The exciter 20, in turn, applies a varying voltage to the field 35 of the main generator 5 tending to correct the output voltage of the main generator.

When the voltage of the main generator increases above a predetermined value, the voltage drop in the resistance 8 is increased and accordingly the negative potential at the input of tube I2 is correspondingly decreased. As a result the final current in the field winding I8 is accordingly decreased so that the exciter 20 generates a correspondingly smaller amount of current for the field winding 35, thus tending to reduce the voltage generated by the main generator 5.

Similarly, when the voltage across generator 5 drops below a predetermined value, the drop in the resistance 8 is accordingly decreased and as a result the negative input voltage through tube I2 is increased, causing a corresponding increase in the current flow in field winding I8. The exciter 20 therefore increases the current fiow through the field winding 35 to increase the voltage of the main generator. In either case, as soon as the voltage of the generator is brought to its correct value, any further increase or decrease of the field current is stopped and the action of the regulator ceases immediately, thus avoiding hunting of oscillations.

Figure 3 shows a regulator adapted for generators of alternating current. Operation of this regulator involves conversion of fluctuations of voltage on the alternating current line 4! into direct current, amplifying these fluctuations, and applying them to the field 42 of an exciter 43 which supplies the main field 44 of the alternating current generator 45, thus controlling the line voltage on the terminals 4I.

The amplifying system is the direct resistance coupled type. All the grid bias and plate voltages may be supplied from taps on resistance 4'! through a single rectifier and filter system operated from the alternator 45 which is being regulated. The filaments of three tubes, 48, 49, and 50, are energized directly by alternating current through individual transformers 5|, 52, and 53 supplied from the same source. The tube 50 is employed in the last stage to supply the field current to the exciter generator 43 whose field 44 is wound to match the direct current plate resistance of the tube 50. This field winding is the only special piece of apparatus used in the system, all the other parts being standard and readily obtainable. It is desirable to use in the last stage a tube with high current carrying capacity and with high mutual conductance. Devices, such as thyratrons, consisting essentially of a gas filled amplifier tube may also be used.

In Figure 3 we have shown a modified system for regulating the output voltage of a generator embodying a new type of amplifier according to our invention. The amplifier in this figure is a modification and improvement over the direct coupled amplifier shown in Figure 2 and is distinguished therefrom basically by a reversal of output phase relative to input phase of the signal current or voltage variations as compared with a rectifier according to the prior art and as shown in Figure 2.

It is known that. in an amplifier wherein the output from the plate of one tube is directly epplied to the grid of the subsequent tube, the

phases of the currents are reversed in each stage. Therefore, with two stages and a consequent double reversal, the phase of the output is exactly the same as of the input; that is, a reduction in the input potential results in a reduction in the output potential. Thus, in Figure 2, if there is a drop in the potential on the lines G l, this drop places a higher negative potential on the grid l3 of tube l2, and with the two stages of amplification a more negative potential on the plate of tube I6. Thus, since the plate of tube I6 is supplied from positive terminal of the rectifier, a lowering of this plate potential sends a heavier current through the field circuit G9, which is the result desired.

However, in Figure 3, an account of the reduced sensitivity of the control element and the need of a higher regulating effect, it is necessary to introduce three stages of amplification, or rather, the output of tube 48 has to be amplified in tubes 49 and 59. Since the reduction in the potential on the line 4i-4i results in a smaller electronic emission, the impedance of the tube 48 increases, and therefore, there is a rise of potential on the plate. With two ordinary stages of amplification followin this tube, there would result a rise in the plate potential of tube 59 and a decrease in the plate current of this tube with a consequent reduction of the line potential, instead of the desired increase.

We have shown, however, as a modification oi the old style amplifier. a novel current connection for the tube 49. Instead of connecting the grid of tube 49 to the plate of tube 48 and fixing the potential of the cathode of tube 49 by connection to potentiometer 28. as shown in Figure 2, we have provided a direct connection from the plate of tube 48 to the cathode of tube 49 and fixed the potential of the grid of this tube by connecting to a tap 63 of the potentiometer 47. At the same time, we have shown a coupling resistor 64 between the plate of tube 48 and a tap point 65. Thus. since the connections to the input of tube 49 are reversed, there is no reversal.

of phase in tube 49 and only one reversal of phase in tube 59. As a consequence the rise in potential of the plate of tube 48 results in the lowering in potential of plate 50 and an increase in its current, which is the desired efiect to bring in the correction of the reduced voltage.

The first tube 49 is operated at a low filament temperature and high plate voltage so as to obtain saturated plate current. This constitutes the control element of this system. Under these conditions the current throu h the coupling resistance 54, between the plate of tube 48 and the grid of tube 49, is nearly independent of the plate voltage, but changes rapidly with the filament temperature and hence with the root mean square value of the line voltage at 4|.

A grid control for the first tube 48 may be substituted for the filament control by using a small portion of the direct current supply from the rectifier as grid bias. but this it is believed controls the average value of the half cycle wave constituting the output of one rectifier, rather than the root mean square value of the line voltage, since the rectifier output voltage is more closely related to this average value than to the R. M. S. line voltage.

The drop of voltage across the coupling resistance 94 is partially compensated for by a small adjustable portion of the rectifier voltage output from the tap 63 and then applied to the grid of the second tube 49, which may have a high amplification factor (a high Thus, a decrease in the line voltage causing a decrease of current through the tube 48 and accordingly a decrease of the voltage drop across 64 makes the grid of the tube 49 more negative, cutting down the current through coupling resistance 54 between tube 49 and 59, and making the grid of the tube 59 more positive and building up the line voltage. An increase in line voltage reverses this process. Resistance 54 may be considered a translating device.

A much higher amplification is necessary in an alternating current regulator than in a direct current regulator since the regulation characteristics of an ordinary alternator are much worse than those of a direct current generator, particularly one which is flat compounded. This higher sensitivity makes the operation rather unstable, for the vacuum tube system is almost instantaneous in its response to small fluctuations in the line, whereas the time lags in the fields of the exciter and the main alternator are quite considerable. These circumstances cause hunting, that is, oscillation of the line voltage about a mean value. To correct for this the regulator is stabilized by a feed-back coupling system composed of a condenser BI and a resistance 62 which reacts on the grid of the first tube 48. This pro-: vides a delay in the response of the regulator, this eliminating its tendency to over-correct.

In operating this current it is necessary to build up the alternator voltage by exciting the main field 44 from a separate direct current supply and then shifting by means of a double throw switch to the output of the exciter generator 43. The starting procedure could be much simplified or made automatic, if desired, by having a selfexciting field on the auxiliary exciter generator 43 with suitable switches or relays for shifting the connections to the regulator when the line voltage approaches normal.

While we have described our new amplifying system as embodied in a regulating circuit for an electric generator, it is understood that it may be used for various purposes wherein it is required to amplify relatively slow variations of electric current or potential and where extended frequency bands are to be amplified or a broad fiat top frequency response curve is required due to the absence of frequency responsive coupling elements, such as condensers and inductance coils.

We claim:

1. A cascade amplifier comprising a plurality of discharge devices each comprising a cathode, anode and grid electrode; a potentiometer having its terminals connected to the opposite poles of a current source; a direct conductive coupling connection from the anode of a controlling device to the cathode of a succeeding controlled device; potential supply connections between the anodes and cathodes of said devices and said potentiometer at such points thereof that successive devices are in parallel to successive separate sections of said potentiometer, and further connections from the grids of said devices to points on said potentiometer to secure proper biasing potential difference between the cathode and grid of the controlled stage.

2. A cascade amplifier comprising a first amplifying device; a second amplifying device, each comprising a cathode, anode and a grid electrode; a potentiometer having its terminals connected to the opposite poles of a supply source;

a direct conductive coupling connection from the anode of said first device to the cathode of said second device; potential supply connections between the anodes and cathodes of said devices and said potentiometer at such points thereof that successive devices are in parallel to successive separate sections of said potentiometer, and further connections from the grids of said devices to points on said potentiometer to secure proper biasing potential difference between the cathode and grid of said second device; and a coupling impedance in the connection from the anode of the first device to said potentiometer.

3. An amplifier comprising a first discharge device; a second discharge device; each of said devices having a cathode and an anode; a potentiometer connected across a source of current supply, said devices being connected across said potentiometer in series, with the anode of said first device being connected directly to the cathode of said second device; a coupling impedance connected between the junction point of said devices and an intermediate point on said potentiometer; a grid for said second device connected to a point on said potentiometer; and means for varying the impedance of said first device in accordance with input signals; and further means for deriving output current variations from said second device.

4. An amplifier comprising a first discharge device; a second discharge device, each of said devices having a cathode and an anode; a source of current and a potentiometer connected therewith; a connection from the anode of said second device to a positive point of said potentiometer; a connection from the cathode of said first device to a negative point of said potentiometer; a direct conductive connection from the anode of said first device to the cathode of said second device whereby said devices form a conductive by-pass circuit around and completely excluding said potentiometer between said positive and negative points; a further circuit connection including a coupling impedance from a point on said potentiometer intermediate said first mentioned points to the junction point of said devices; a grid for said second device; a further connection from said grid to another point on said potentiometer intermediate said negative point and said first intermediate point; means for varying the impedance of said first device in accordance with input signals and further means for deriving output current variations from said second device.

5. An amplifier comprising a first discharge device; a second discharge device, each of said devices having a cathode and an anode; a source of direct current and a potentiometer connected therewith; a first connection from the anode of said second device to a positive point on said potentiometer; a further connection from the cathode of said first device to a negative point on said potentiometer; a direct connection from the anode of said first device to the cathode of said second device whereby said devices form a conductive by-pass circuit around and excluding said potentiometer between said positive and negative points; a further circuit connection including a coupling impedance from a point on said potentiometer intermediate said first mentioned points to the junction of said devices; a grid for said second device; a connection from said grid to a further point on said potentiometer intermediate said negative point and said first intermediate point; means for varying the impedance of said first device in accordance with input signals; and a translating device inserted in said first mentioned circuit connection.

6. In an amplifier, a first discharge device, a second discharge device having a high amplification factor, each of said devices comprising a cathode and an anode, potentiometer means arranged to be energized from a source of current supply, said devices being connected to said potentiometer means in series with the anode of the first device connected directly to the cathode of the second device, an impedance connected between the junction of said devices and an intermediate point on said potentiometer means, a grid for said second device connected to a further intermediate point on said potentiometer means, means for impressing an alternating controlling potential upon said first device to set up a direct current voltage drop across said impedance varying in accordance with the amplitudes of the control potential, and further means for deriving output current variations in accordance with said varying voltage drop from said second device.

LAL C. VERMAN. LORENZO A. RICHARDS. 

